Multiple photocell structure



4 c. F. TAYLOR ETAL 2,663,134

MULTIPLE PHOTOCELL STRUCTURE Filed Feb. 15, 1952 2 Sheets-Sheet 1 Inventors:

Clement 1 Taylor;

Walton E. Bmggs John F. \X/earg 7 f 2, 1954 c. F. TAYLOR ETAL 2,668,184 MULTIPLE PHOTOCELL STRUCTURE Filed Feb. 15, 1952 2 Sheets-Sheet 2 Patented Feb. 2, 1954 MUL'rrrLE *PHOTOCELL s'rnUo'r-Uml fillem utFt-Tarlcrlhynn, WaltonE. Brigg -r 1m Center an John ry, L o le, ass guors to General Electric Company}, aQQrpQra Qnof New York Application February 15, 1952, Serial No. 271,746

Dbls .a pair. .of similar, spiraleshaped photocells which are interlcared or nested together, .the .conroluticns of one cell occupying the spiral Sp ce between the turns of the other cell, with the sensit'n/e sur-fiaces of the .cells lying .a common Blane. These cells must. be insulated from each other, and the present invention includes one method or manufacturing such composite lthotocells and the resulting structure. The intention. is applicable generally .to multiple photocell structures where twoior more cells are fabri- Gated. into a. unitary assembly with their light sensitive surfaces in a common plane and the cells insulated from each other.

An object of the invention is to. provide a multiple photocell unit .01 the type described so arranged that. the set of separate photocell elements comprising the unit will have a linear response characteristic in orderthat the reading of the color control meter will be independent of the intensity-o1 the illumination.

A further object. is to provide a multiple photo cell structure capable of producing an output independent of the direction, at which the. illumination-strikes the unit.

A still turther object is to p ovide a multiple photocell unit spcciallyadapted to cooperate with spiral masking means so as to obtain along range of movementof the masks, as described more particularly in the .copending appl cation of. Clement F.-"I.ayl0r,-seria1No- 21'5A14; iilled March .7, 1952, tl Mul l Ma ked Ph tocell Structure, assigned to the some assignee as. the present application 7 Other objects and advantages will become apparent from the following description t ken in connection with the accompanying drawings i which Figure 1 shows the plan shape of each spiral photocell element,'Figure :2 is a plan view of .two spiral photocell units in assembled relatlon, Figure 3 is a sectional view taken along the line 8*: in Figure 2, Fig. 4 is an enlarged 2v secti nal view ofaahort h l the mu ti le-en locell structure. how s the. nature of. m filled tion pbotwccn the cells wh h mechan ca l them into a single structure yet kee s th m silhstantially insulated electrically, Figure 5. {so gotail elevation showine one ossib e mod ficat or the cell as emb y o Floors 6 is en enlar ed sect onal View, s mewhat liis- .ure. 4, sh win a modifi et n,v and .zEl -u is an enlar ed ec ional modification.

"Features whic re con dered to enor end patentable wil h pointed ut t e-claims eopcnded hereto.

In Fi ure 1 th re isshown. thehlan t rm of the steel blank or- --bac ola e- .l o one or th sp a photocell-s. 'lhe plate l is soshapedand dimensionedthat it; maybe nterlinked or nested to ether with an identical p ate, w h the turn lone substantially fil i g; the spac be ween-th turns of the other, as will be ap arent. in Fig. g, where. 2. and :3 r present two spira hotoeells each having a backplate shaped asv in Fi 1. The hackplates I la for the two. cells are dimensioned so that when assembled asv in Fig. ,2, there. is a gap of about 1.02 inch between the adjacent ed es at all points. It will'be evident that the two hackplates, :being identical, may be stamped with they same punch and d113, Each spiral as here represented has approximately two. complete turns and each has a st w at .4 in ts o ter pe iphery located ppro mately-1w from its outer end, and is otherwise shaped so that, when the two spirals are interlinked, the complete structur will ha e a circular outlin with notches at opposi e points the per he y between the step .4 in one ell and the outer end of the other cell- Su h p riphe al notches. may e us d to a commodate the connect n wires an erm nal. cl ps (no shown).

The inner ends of the matching spiral cells are shaped f hutt n relat onship, w flihalf circ e. cut-out (shown at 5-). in each, so that a ir u a uide pe t not shown) ma be inserted therein during assembly to assist in obtaining uniform spacing between cell blanks.

lhe first step in the manufacture or the spiral cells, after the backplates are available, is .to cover one surface of each plate with a thin coating of selenium, for example, and assemble Ithe showiha soo he coated blanks in the pattern they are to occupy in the finished structure on a flat surface or flatbottomed tray with their selenium coatings in alignment in a common plane and with suitable guides, such as the sides of the tray, correctly positioning and supporting the outer convolutions of the spirals. As a matter of fact, the selenium coating may be applied either before or after the plates are assembled in interlinking relation. The assembled and coated parts are then subjected to pressure at right angles to their surface by a fiat surfac'ed press, the pressure being not less than 100 pounds per square inch and perhaps as high as 1000 pounds per square inch, and at a temperature of from 1-25 to l 9 0 degrees C. The selenium softens and is pressed until the selenium coating on the flat surfaces of the plates is reduced to a thickness of between 0.003 and 0.005 inch, and the excess selenium completely fills the 0.02-inch gap between the spiral plates. The pressure and temperature used, the thickness of the selenium coating, and the gap dimension are not very critical, so long as the result is a uniform compact thickness of at least 0.003 inch of seleniu on the upper 'suifaceand a complete filling of the gap between the plates with selenium. This firmly unites the two backplates with a single mechanical unit. 4 r

Any excess selenium on t e outer circumferential edges of tire backplates is then removed, and the selenium on the" surface of the plates is converted to the light-sensitive crystalline form, as by baking in an oven, at a temperature of about 218C. for the proper length of time. For some uses and circuit arrangements, the selenium in the gap between the two backplates may be left in the crystallized state and it, therefor'e', forms a low' resistance bond between the backplates of the cells. For other purposes and circuits, the rystallized selenium between the cells does not offer sriifieient resistance, and in such cases it can be given a much higher resistance by converting the selenium in the gap from the crystalline to the amorphous form. Such conversion may be accomplished either before or after the exposed selenium surface coating is processed in the usllal way for rendering thecell photo-sensitive; but we generally prefer to do it before." Hence, where the crystallized selenium between the cells is to be" converted to the amorphous form to increase its resistance, as required in' the color control meter of the above identified application of Stimson and Bakke, we prefer to inake this the next step. The thin layer of selenium on the top exposed surfaces of the cells" must, however, remain in crystalline form.

The selenium in the gap between the plates may be changed from crystalline to amorphous form, without substantially altering the selenium in the surface layer, by passing'an electric cu rent between the backplates and across the gaps to heat the selenium in-ltlie gap above its melting point of about 220 C. If then the structure is quickly cooled, the selenium in the gaps will retain the amorphous form and will be of high resistance. The resistance between the backplates may be increased to'about' 50,000 ohms in this way.

The electrical connections" for this step may be as represented diagrammatically in Fig". 3; and for the cell combination'des'cribed herein", which had' an outer diameter of about two inches, we

found that passing a current or about 1 9411- 75 the two spiral strips,

peres for 30 seconds between the cell plates was sufficient. More correctly, the current at the start of this 30 seconds is about 1 /2 amperes and decreases as the change takes place. This heating current does not tend to cross through the surface layer 1 of the selenium, which therefore remains well below its melting point and retains the crystalline form.

Another method of melting the selenium in the gaps is to pass an electrically heated wire through the gap" from end to end, thewire being maintained at right'angles to the plates like a cheese cutter and moved along as fast as the selenium in contact therewith melts. As soon as the hot wire has passed the melted selenium cools in the amorphous form and most of it is retained in the gaps to bond the plates together. The nest step in preparing the cells for use is to sputter the surface selenium 1 with a layer of a conductive material, such at platinum, etc., as describedfor example in United States Patent No. 2,296,670, issued September 22, 1942, and assigned to the same assignee as the present application. This conducting surface layer is applied over both cells but not on the outside edges, and must be cut through above the gap between the plates to electrically separate the two cells. A sharp instrument such as an engraving tool may be used for this purpose, and a out between 0.001 and 0.01 inch deep is satisfactory.

Fig. 4 represents an enlarged cross section view of the cell combination, taken through one of the gaps and adjacent cell parts. The two spiral steel backplates or cell blanks are shown at i, la, the two cells at 2, 3. The amorphous selenium in the gap between the cells is identified 6, the crystalline selenium surface layer at I, the sputtered conductor layer 8, and 9 is the cut for separating the conductor layers of the two cells.

In order that all portions of the photo' sensitive selenium surface will have a low-resistance path to tlie'terminal's of the photocell unit, there is provided a rather complicated network of collector strips on the top surface of the conductive layer 8, which strips may be conveniently applied to the conductive layer 8 by spraying a metal, such as cadmium, with suitable masking arrangements. The shape of these collector strips is shown in Fig. 2, in which I l is the spiral collector strip for cell 2 and I2 is the collector strip for cell 3-, These collector strips are in the form of a double spiral dividing the spiral cell into three parallel strips of roughly equivalent area. Adjacent the outer ends of the spiral cells, these collector strips have three, instead of two, parallel paths "so that all portions of the light sensitive area of the cells have direct acess to the low resistance collector strip. It is also to be noted that these collector strips widen out adjacent the step 4 to form the terminal portions I3a, l3b. These terminals are adapted to be engaged by contact clips (not shown) connected to the lead wires for the external cirsuit. The back surface of the backing plates carries similar sprayed cadmium terminals identified in Fig. 2 in dotted lines at Ma, [4b.

Certain production difficulties have been traced to the fact that the cadmium collector strips H, [2 may be imperfectly sprayed, so that thereare open-'circuited portions which increase the overall resistance of the cells. To provide low resistance paths around such open-'circuited portions of the collector strips, there may be provided additional radial shunt strips connecting as shown in Fig. 5 at In separate cell structures roses necessary if the measureme and I In. These radially disposed bridging strips plete network, the resistance of which will be substantially unaffected by any local disconti'nui ties in the spiral collector strips.

A useful rule of thumb in designing the net'- 'work of conductive collector strips II', a, [2, 12a is that no portion of the photosensitive area of the cells shall be more than .100 inch from a collector strip. It may be found desirable to have a distance as small as about .050 inch from a collector strip to each portion of the photosensitive area. Of course it must be remembered that the collector strips mask a certain amount of the photosensitive area. Therefore, increas'- ing the number of collector strips reduces the effective area of the photosensitive surface. Thus a balance must be struck between havin a sufiicient network of collector strips to avoid the adverse effect of any discontinuities in the strips, yet not covering so much area as to reduce the sensitivity of the cell. The suggested spacing. of 1050 to AC0 inch from the collector strips to all portions of the photosensitive area, with the bridging strips Ha, Ha spaced about inch apart, appears to effect a good compromise.

After the cadmium collector strips have been applied, the top surface of thephotoc'ell unit is protected by a coating of transparent lacquer to (Figs. 2 and 4).

The cell structure of our intention where the layer 6 between the cells is rendered amorphous, so as to have high resistance, may have the cells connected in series relation without any danger of short-'circuiti'ng a cell. This is possible because of the very high resistance between cells. In applications where the tens are to be connected in a differential circuit with the backplate terminals connected together, that is, with the cells in parallel, it is unnecessary to change the selenium layer 6 between the cells from the crystalline to the a orphous condition. in either case the method of manufacture by the applioati'on of heat and pressure to the selenium coating, which operation fills the space between the backplates under pressure provides a rugged, integral, multiple photocell structure where the are cemented together in a predetermined, precisely spaced relation as desired for obtaining accurate light cbmponeht measurements. I

A multiple photocell unit in accordanc with the invention has the extremely important asvantage of exposing the active photosensitive area or each cell at the same average distai'ioe from the light source regardless of the direction from which the illumination falls on the ten. This is extremely important in illumination color measurements for photographic purposes where many different types of light "are e countered. Another important advantage is that a linear response characteristic is aehievea'wheh the two cells are connected in series, for ineas'uri'ng the ratio between two different components of the illumination, by reason of the special arrangeinent of the collector strip network, which provices substantially equal access for the photoelectric current 'fro'in all parts'of the photosensitive surface to the low resis'taj'nce' collector strips. Thus the resistance of the very thin eehshetiye surface coating 8 does not arrest the electrical characteristics i the tens; This is at is to be independent of the intensity of .the'llluniination. The spiral configuration of the photocells adapts them for effective cooperation with the spiral mask system of the above-identifiedapplication Serial No. 275,414.

While only one form of the invention has been described specifically herein, it will be obvious to those skilled in the art that the arrangement may be applicable to multiple photocell units having three or more interleaved spiral cells. The precise shapeof the cells, the pattern of the collector strips required to provide low resistance access to all portions of the photosensitive surface, and. the arrangement of the terminal portions of the collector strips may obviously take many equivalent forms.

It will also be apparent that these complementary photocells may be made by other processes than that disclosed herein. For instance, as shown in Figure 6, a multiple photocell having the configuration shown in Fig. 2 could be made by fabricating a photosensitive disk, then sawing it into two spirals, 2a and 3a,- and securing the two spirals in spaced relation to each other by embedding them in a suitable plastic cement :5 or other insulating bonding material. Such method of manufacture has the important advantage that any local non-uniformities in photosensitive activity would likely be common to both cells.- In other words, any non-uniform area of substantial size would extend from one spiral across to a portion of the other spiral so that both cells would be affected The first' described method of manufacturing the spiral cells, by fabricating separate backplates, coating them with selenium, and sensitizing the'selehium coating on both cells at the same time,'would share this advantage to someextent. Fabricating the backplates separately has the advantage of avoiding the complicated sawing operation required to divide a circular cell into two spirals.

Still another method of fabricating the multiple spiral photocell, illustrated in Figure 7, would be to secure the separate spirals 2b and 3b to a molded plastic backplate It having a spiral, projection I! on one face which serves to locate and space the spirals from each other.

It is of course desired to cover by the appended claims all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

'1. A multiple photocell structure comprising two similar spiral-shaped photocells interlinked in a comm-oh plane so that spiral portions of one cell lie between Spiral portions of the'othr cell and spaced from each otherby g ps of aphroxhhat 1 ;0. 2 inch filled with amorphous seleniuinfwhich insulates the cells from each other and unites the cells into one mechanical structure, the outer ends of said spiral cells being shaped such that the outline of the complete structure is substantially circular.

2. A multiple photocell structure comprising a pair of similar spiral shapedf photocells, said cells being interlinkedin a common plane such that spiral portions of one cell lie between spiral portions of the other cell, each cell having a metal backplateand a crystalline selenium coating con ronting to the spiral shape of the cell, the interlinked adjacent surfaces-of such backplates being separated from eac other by 'a spa ing of the order of 0.02 inch, and the gaps thus formed being filled with amorphous selenium whichis continuous with the seiemum surface coating of the bells, said amorphous selenium insulating the cells from each other and uniting said cells into one solid mechanical structure.

3. A multiple photocell structure comprising a pair of similar spiral s'hape'd cells, said cells having' spiral metal backplates interlinked with each other so that spiral portions of one lie between spiral portions of the other in the same plane and spaced apart by gaps of the order of 0.02 inch, the upper surfaces of said plates being coated with light sensitive crystalline selenium and the gaps between the plates being filled with selenium, the crystalline selenium on the lightsensitive surface and the selenium in the gaps being continuous and uniting said cells into a solid mechanical structure, terminals adjacent the outer spiral ends of said cells, and spiralshaped conductor strips for the selenium coated surfaces of said cells leading from said terminals to adjacent the inner spiral end portions of said cells.

4. A multiple photocell structure comprising two separate spiral shaped photocells having photosensitive surfaces disposed in a common plane, the convolutions of one cell lying in the spiral space defined between adjacent cell convolutions and spaced therefrom by a gap of substantially constant width along the spiral length of the cell, and means securing said cells in fixed relation to each other, the outer convolutions of the cells being shaped so the outline of the photocell assembly is generally circular.

5. A multiple photocell structure comprising a plurality of complementary spiral photocells interleaved with the convolutions of one cell lying in the spiral space defined between adjacent cell convolutions, the fiat top surfaces of all cells lying in a common plane and having a coating of photosensitive material, adjacent convolutions being spaced from each other by a gap of substantially constant width along the spiral length of the cell, means securing the separate cells in fixed relation to each other, the outer convolutions of the spiral cells being modified so that the perimeter of the composite cell unit is of generally circular configuration.

6. A multiple photocell structure comprising at least two separate photocells with photosensitive surfaces disposed in a common plane, means securing said cells in fixed relation to each other, each cell having a transparent conductive coating on the photosensitive surface thereof and a network of narrow low resistance collector strips disposed in contact with said conductive coatin no portion of the photosensitive surface being more than .100 inch from the nearest collector strip portion.

'7. A multiple photocell structure comprising at least two spiral cells of similar shape, each cell having a conductive backplate member coated on one surface with photosensitive material covered by a transparent layer of conductive material, the several cells being disposed in the same plane with the convolutions of one cell lying in the spiral space defined between the other cell convolutions with a gap of substantially constant width separating adjacent convolutions, means securing said backplates in fixed relation to one another, each cell having at least one narrow low resistance collector strip disposed in contact with said conductive layer and extending substantially the entire spiral length of the cell whereby the entire photosensitive surface thereof has a path of low electrical resistance to the external convolution thereof, the collector strip of each cell having at least one enlarged terminal portion of conductive material on the outer convolution thereof, whereby the relative electrical output of the cells is substantially independent of the intensity of illumination and of the direction at which light falls on the cell.

8. A multiple photocell structure comprising a plurality of spiral cells, each cell having a conductive backplate coated on one surface with photosensitive selenium covered by a transparent surface layer of conductive material, the several cells being disposed in the same plane with the convolutions of each cell lying in the spiral space defined between the other cell convolutions with a gap of substantially constant width separating adjacent convolutions, said gap being filled with plastic material bonding the backplates into an integral mechanical structure, each cell having at least two parallel low resistance collector strips disposed in contact with said conductive layer and extending substantially the entire length of the spiral, whereby the entire photosensitive surface of the cell has a path of low electrical resistance to the external convolution thereof, a collector strip of each cell having at least one enlarged terminal portion of conductive material, whereby the electrical output of the cells is substantially independent of intensity of illumination and of the direction at which light falls on the cell.

9. A multiple photocell structure in accordance with claim 8 and including radially disposed shunt collector strips connected across the parallel spiral collector strips at spaced intervals along the spiral length thereof, whereby all portions of the photosensitive surface have direct access to the low resistance network of collector strips.

10. A multiple photocell structure comprising at least two spiral cells of similar plan shape, each cell having a conductive backplate member coated on one surface with photosensitive crystalline selenium with a transparent surface layer of conductive material, the several cells being disposed in the same plane with the convolutions of one cell lying in the spiral space defined between the other cell convolutions with a gap of substantially constant width separating adjacent convolutions of the respective cells, said gap being filled with selenium continuous with the surface coating and bondin the backplates into an integral mechanical structure, each cell having at least one narrow low resistance collector strip disposed in contact with said conductive layer and extending substantially the entire length of the spiral whereby the entire photosensitive surface of the cell has a path of low electrical resistance to the external convolution thereof, the outer circumferential edge of each cell defining a circular are so that when in interleaved relation the multiple cells have a generally circular outer configuration, said outer circular arc portion of each cell terminating at either end in a radially disposed step portion spaced circumferentially from a corresponding step portion of the adjacent cell to define a notch in the generally circular contour of the unit, each collector strip being connected to at least one enlarged terminal portion of conductive material disposed on the outer convolution of the cell adjacent one of said steps.

11. A multiple photocell structure comprising a plurality of complementary spiral photocells interleaved with the convolutions of one spiral cell lying in the space defined between adjacent c ntelut onsef e. om lementa y cells. wi h the flat top. surfaces ofall cells lying in a common plane and adjacent convolutions spaced from each other by a gap of substantially'eonstant width on the order of Q2} inch, a lajyer of photosensitive selenium covering the flattqp surface of" the cells and filling the gaps between cells whereby they are bonded intozalh-integralinechanicall unilithe outer eonvolu'tiens of the spiral cells being shaped so that the, circumference of the composite cell unit of generally circular QRQ E QQ lr r 12. A multiple photocellstructure comprising at least two spiral cells of similar shape, each cell having a conductive backplate member coated on one surface with photosensitive crystalline selenium covered by a transparent surface layer of conductive material, the several cells being disposed in the same plane with the convolutions of one cell lying in the spiral space defined between the other cell convolutions with a gap of substantially constant width separating adjacent convolutions, said gap being filled with selenium continuous with the surface coating and bonding the backplates into an integral mechanical structure, each cell having at least one narrow low resistance collector strip disposed in contact with said conductive layer and extending substantially the entire length of the spiral whereby the entire photosensive surface of the cell has a path of low electrical resistance to the external convolution thereof, th collector strip of each cel1 having at least one enlarged terminal portion of conductive material disposed on the outer convolution thereof, whereby the relative electrical output of the cells is substantially independent of intensity of illumination and of the direction at which light falls on the cell.

13. The method of constructing a multiple photoelectric cel1 unitary structure which consists in taking a plurality of metal backing plates of the same thickness and of the siz and shape of the cells to be formed, covering one fiat surface of such plates with a thin layer of selenium, assembling such plates on a fiat surface in the relative positions which they are to occupy in the finished structure and with a spacing between the plates on the order of 0.02 inch, applying pressure at right angles to the flat surface of the plates while the plates and selenium coatings thereon are at a temperature between 125 and 190 degrees C. and thereby compressing the selenium coatings to a thinner uniform thickness and forcing excess selenium into the space between the plates completely to fill the same and unite the selenium covered plates into a solid mechanical structure, treating the selenium surface of such structure to convert the same for photoelectric cell use and then cutting into only the treated surface above the selenium filled spaces between the plates to form electrically separated photocell surfaces conforming to the pattern of the plates.

14. The method of constructing a multiple photoelectric cell unitary structure which consists in taking a plurality of metal backing plates of the same thickness and of a size and shape of the cells to be formed, covering one flat surface thereof with a thin layer of selenium, assembling such plates on a fiat surface in the pattern of the cells to be formed and with a spacing of at least 0.02 inch between the plates, applyin pressure at right angles to the surface of the plates while the plates and selenium coating thereon are at a temperature between 125 and 190 deelenium lat s o. r ysle. eetrs llr msula esbet ae: hal eallyun elel qlgcell 15. The method of constructing a multipleoteeel un t which consi in forming a D rality of conductive backplates of complementary plan shapessuch .ithall they may be disposed in interleaved relation with gaps of substantially constant width therebetween, covering one fiat surface of the backplates with a thin layer of selenium, assembling the plates on a fiat surface in adjacent relation with gaps of substantially constant width therebetween, applying pressure to the selenium at an elevated temperature sulfioient to reduce the selenium surface coating to a thin uniform thickness and to force excess selenium into the gap between backplates whereby the plates are mechanically bonded together, converting the selenium to light-sensitive crystalline form, converting the selenium in the gaps between plates to high-resistance amorphous form by melting only the selenium in the gaps and then cooling it rapidly, applying a transparent conductive coating over the crystalline selenium surface, and making an incision extending entirely through the crystalline selenium surface layer, said incision lying over and extending the length of the gaps between plates to electrically insulate one cell from the other.

16. The method of constructing a multiple photoelectric cell unit which consists in forming a plurality of conductive backplates of such complementary shape that they can be disposed adjacent one another in interleaved relation with gaps of substantially constant. width therebetween, covering one flat surface of the backplates with a thin layer of selenium, assembling the plates on a fiat surface in interleaved manner with substantially constant gaps between cells, applying pressure to the selenium coatings with the plates and selenium at an elevated temperature to compress the selenium surface coating to a thin uniform thickness and force excess selenium into the gaps between backplates whereby the plates are integrally united, treating the surface coating of selenium to convert it to photosensitive crystallin condition, treating the selenium in the gaps to convert it to the amorphous condition, and electrically separating the cells by making an incision through the photosensitive surface coating, said incision lying above and extending at least to the amorphous selenium in the gap between the backplates.

17. The method of constructing a multiple photocell unit which consists in forming a plurality of conductive backplates of such complementary shapes that they can be disposed adjacent one another in interleaved relationwith gaps of substantially constant width therebetween, covering one fiat surface of the backplates with a layer of selenium, assembling the plates on a flat surface in interleaved relation with substantially constant gaps between plates, applying pressure to the selenium coating with the plates and selenium at an elevated temperature to compress suriasa an then setting throu h s es eetin ever the elenium f lled a s betw en the the selenium surface coating to a thin uniform thickness and force excess selenium into the gaps between plates whereby they are integrally united, treating the surface coating to convert it to photosensitive crystalline condition, treating the selenium in the gaps to convert it to amorphous condition, applying a transparent conductive coating to the photosensitive selenium surface, and electrically separating the cells by making an incision through the conductive coating and through the photosensitive surface coating, said incision extending along and at least to the amorphous selenium in the gaps between the plates.

"' CLEMENT F. TAYLOR.

WALTON E. BRIGGS. JOHN F. WEARY.

ReferencesQited -in the file of this patent UNITEDSTATES PATENTS umbe Nm Dat Chewy;v Ma 1923 Wald; Oct. 8.1940, Hewlett Sept. 22', 1942 Lamb f Dec. 15, 1942 Kipphan Sept. 28, 1943 FOREIGN PATENTS Country Datev Great. Britain May 29, 1928 

